Heat-sensitive stencil paper

ABSTRACT

A heat-sensitive stencil paper comprising a film made of a vinylidene chloride-vinyl chloride copolymer and adhesively lined with a support sheet consisting of a porous thin sheet of paper by the use of a polyvinyl acetate adhesive which is applied thereto in amount ranging from about 0.5 to about 5.0 gr./m.2 in terms of the solid weight of adhesive, and being adapted to form a printing image consisting of perforations in said film when exposed to infrared light.

United States Patent inventors Keishi Kubo;

Kiyoshi Sakai, both of Tokyo, Japan Appl. No. 762,352 Filed Sept. 16, 1968 Patented Oct. 5, 1971 Assignee Kabushiki Kaisha Ricoh Tokyo, Japan Priority Oct. 6, 1967 HEAT-SENSITIVE STENCIL PAPER [56] References Cited UNITED STATES PATENTS 3,149,563 9/1964 Wartman et a1. l01/l28.4 X 3,267,847 8/1966 Hayama et al. 101/1282 Primary Examiner-David Klein Attorney-Woodhams, Blanchard and Flynn ABSTRACT: A heat-sensitive stencil paper comprising a film made of a vinylidene chloride-vinyl chloride copolymer and adhesively lined with a support sheet consisting of a porous thin sheet of paper by the use of a polyvinyl acetate adhesive which is applied thereto in amount ranging from about 0.5 to about 5.0 grJm. in terms of the solid weight of adhesive, and being adapted to form a printing image consisting of perforations in said film when exposed to infrared light.

1 HEAT-SENSITIVE STENCIL PAPER BACKGROUND CF THE INVENTION 1. Field of the Invention The present invention is related to a heat-sensitive stencil paper of the type in which a resinous film made of vinylidene chloride-vinyl chloride copolymer is adhesively attached by an adhesive to a porous thin sheet of paper serving as the support sheet, wherein said adhesive consists principally of polyvinyl acetate and wherein said adhesive is applied in amount ranging from about 0.5 to about 5.0 grJm. in terms of the solid weight of the adhesive.

2. Description of the Prior Art Known heat-sensitive stencil papers of the type in which a film made of a thermoplastic synthetic resin is adhesively lined with a porous tissue and is adapted to form a printing image, such as letters, consisting of perforations in said film when said stencil paper is exposed to infrared light include those proposed by, for example U.S. Pat. Nos. 2,808,777 and 3,267,847. The former of these U.S. Pats. teaches a method for manufacturing a printing sheet from a stencil paper, wherein films made of several kinds of thermoplastic synthetic resins and a few kinds of porous tissues are disclosed as the materials constituting the stencil papers of said patent. The latter of said U.S. Pats. discloses a method for manufacturing stencil papers by the use of vinylidene chloride-vinyl chloride copolymers of specific composition ratios and specific porous tissues. Both of these U.S. Pats. refer, relatively in detail, to the sheet materials which are used in the manufacture of stencil papers, but they altogether fail to mention the choice of the adhesives which are employed for adhesively attaching them together. However, it is extremely difficult to make a proper selection of the adhesives to be employed in the manufacture of stencil papers. However well suitable the resinous film and the porous thin sheet of paper may be as the materials for the manufacture of stencil papers, the inadequacy in the amount and/or selection of the adhesive employed will affect greatly the quality, such as perforability, of the product stencil papers. Also, an excess in the amount of the applied adhesive will lead to the failure in the acquisition of good effect of printing. Furthermore, even where-the adhesive employed is of good adhesion and where, accordingly,the adhesive is used in a limited amount, it often occurs that the shelf life of the product is reduced owing to external factors such as the ambient moisture which is easily absorbed by certain types of adhesives.

SUMMARY OF THE INVENTION It is, therefore, the object of the present invention to provide a heat-sensitive stencil paper of the type in which a film made of a synthetic resin consisting of a vinylidene chloridevinyl chloride copolymer is adhesively attached to a known porous thin sheet of paper which serves as the support, by the use of an adhesive and that a clear printing image consisting of perforations is formed in said film by exposing said stencil paper to infrared light, wherein said adhesive consists of a polyvinyl acetate resin and wherein said adhesive is used in an appropriate amount.

Conventional adhesives include those made of materials such as synthetic resins, rubbers, starches and rosin. However, those which are most often used, among the various resinous adhesives, are represented by those intermediate polymers from coldsetting resins (polymeric resins prepared by the use of catalyst) or from thermosetting resins. Adhesives made of other materials may be divided into numerous complicated groups if this division is performed minutely. Accordingly, there are innumerable kinds of adhesives and also they are used for a variety of purposes. For this reason, it is impossible to select proper adhesives which satisfy the specific purpose as is aimed at by the present invention from among the countless number of adhesives, unless painstaking inventive efforts are exercised.

For example, thermosetting resins include a large variety of resins such as phenolic resins, epoxy resins, alkyd resins and many other kinds of resins. When resins of these groups are employed in the manufacture of heat-sensitive stencil papers, there invariably occurs the phenomenon that the product stencil papers become hardened. This hardening of the product is caused by the hardening of the layer of adhesive which is located intermediate of the laminated sheet materials. For this reason, the product structure feels stiff or starchy and is poor in the ability to form perforations, and thus, the product is not suitable for being used as a commercial article. Some of the thermosetting resins possess the property, depending on the degree of polymerization thereof, of sofiening when heat is applied thereto. However, polymerization of these resins will proceed due to their exposure to continued I heating or as a result of their being left to stand for an extended period of time, and accordingly, these resins cannot be applied to the present invention either.

Rubber adhesives include those made of natural rubber and synthetic rubbers (polychloroprene, niu'ile, butadiene-styrene rubbers). These rubber adhesives are provided in various forms such as solutions in which rubbers are dissolved in solvents, or they are provided in the form of emulsions. These rubber adhesives are good in adhesion but they are not necessarily satisfactory in the ability of forming perforations.

Starch adhesives and proteinocesus adhesives not only are inferior in adhesion but also they have many problems in regard to their waterproofness and other aspects, and accordingly, they can not be applied to practical use either.

Considering that rubber adhesives are superior to the rest of the aforesaid various groups of adhesives, a test was conducted by us on the following various commercial adhesives, i.e. an aqueous synthetic rubber latex adhesive (trade name: Bond 2,100, a product of Gisuke Konishi and Co., Ltd. of Japan), an adhesive in the form of a ketonic solution of a synthetic nitrile resin trudename: Bond G l00,a product of the same company), an adhesive in the form of a ketonic solution of a synthetic chloroprene resin v(trade name: DlABOND 1,633, a productof Nogawa Chemical Co., Ltd. of Japan), by varying the amount of these adhesives employed. lt was found, however that these known adhesives were satisfactory in adhesion (some of them showed a very good adhesion), but, as stated above, they equally showed a markedly poor perforability. Even when the amount of the applied adhesive was reduced to the order of 2.0 gr./m.', no sufficient perforations were formed and this means that the stencil papers containing these adhesives were poor in the resolving ability. As such, these adhesives were not usable for practical purposes.

In addition to the aforesaid adhesives made of thermosetting resins which are one of the many adhesives made of synthetic resins, there are those made of thermoplastic resins which have been developed rapidly of late. Adhesives made of thermoplastic resins also vary widely in type and property. An extensive research was conducted by us, on the adhesives made of thermoplastic resins, and as a result, it was discovered that an adhesive consisting principally of polyvinyl acetate was quite effective for the purposes of the present invention. Although the reason why polyvinyl acetate adhesive exhibits a good result has not been elucidated in detail, it is presumed that this good result is due to the low softening point and the narrow range of melting temperature of this resin.

The adhesives made of polyvinyl acetate resins which are used in the present invention include not only those adhesives in the form of both emulsions and solutions of vinyl acetate homopolymers, but also those adhesives in the form of both emulsions and solutions of a copolymer of vinyl acetate and a monomer of other type, such as vinyl acetate-acrylic or acrylate copolymer, vinyl acetate-vinyl-pyrrolidone copolymer, vinyl acetate-vinyl chloride copolymer and vinyl acetateethylene copolymer.

As is the case with rubber adhesives, a better perforability is obtained from the use of a smaller amount of applied adhesive with the vinyl acetate adhesives. However, there is a very adhesion. While there are slight differences in the properties between a vinyl acetate adhesive of one type and that of another type, such a difference can cause no problem provided that they are used in'arnount ranging from 0.5 to 5.0 grJmF.

The preferred polymerizing proportion of vinylidene chloride to vinyl chloride, both of which constitute the vinylidene chloride-vinyl chloride copolymer employed in the present invention, is in the range of 70-30/95-5.0. The materials of the porous thin sheets of paper which are employed in the present invention include natural fibers such as the fibers of paper mulberry, mitsumata and manila hemp, synthetic fibers such as those of rayon acrylic resin, nylon and polyvinyl alcohol, and mixtures thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1 An adhesive in the form of a methanolic solution of polyvinyl acetate (trade name: GOHSENYL M50-Y-5, a product of Nippon Synthetic Chemical Industry Co., Ltd. of Japan) was diluted with methanol to a viscosity of about 30 cp., and thus, an adhesive was prepared. Using this adhesive, a resinous film consisting of a vinylidene chloride-vinyl chloride copolymer and having a thickness of 10;; was adhesively attached to a support consisting of a porous thin sheet of paper of p.in thickness and l3gr./m.' in weight by the use of a known laminating machine and in such a way that the deposited amount of said adhesive was 2.0 gr./m..

On the heat-sensitive stencil paper thus obtained was placed an original carrying printed images on both sides, and they were exposed to infrared light at the side of the porous thin sheet of paper to thereby form perforations in the film, and thus, a perforated printing sheet for printing purpose was made. Printing was conducted by the use of this perforated printing sheet on a commercial rotary stencil machine, with the result that a print carrying a clearly formed printed image which was a literally faithful reproduction of the original image was obtained. After printing more than 2,000 copies,

there was noted no appreciable loss of clarity of the printed images.

EXAMPLE 2 An adhesive in the form of an aqueous emulsion of vinyl acetate (trade name: Bond CV 100, a product of Gisuke Konishi and Co., Ltd. of Japan) was diluted with water to a viscosity of about 70 cp. Using the resulting adhesive, a resinous film consisting of vinylidene chloride-vinyl chloride copolymer and having a thickness of 8pwas adhesively attached to a support sheet consisting of a porous thin sheet of paper of 30p.in thickness and l 1 gr./m. in weight by the use of a laminating machine and in such a way that the amount of the deposited adhesive was 4 gr./m. in terms of the solid weight of the adhesive. The result was as good as that noted with the product obtained in Example 1.

EXAMPLE 3 An adhesive in the form of an aqueous emulsion of modified vinyl acetate (trade name: Cemedine No. 630, a product of Cemedine Co., Ltd. of Japan) was diluted with water to a viscosity of about 150 cp. The resulting adhesive was used in adhesively attaching a resinous film of a vinylidene chloridevinyl chloride copolymer of l2p.in thickness to a porous thin sheet of paper of 40p.in thickness and 15 grJm. in weight. The result was as good as those results obtained in the preced ing two examples.

What is claimed is: 1. In a heat-sensitive stenc|l paper comprising a synthetic resin film, the principal component of which is a vinylidene chloride-vinyl chloride copolymer, a porous thin fibrous sheet as a support for said film and an adhesive layer for securing together said film and said support, the improvement wherein said adhesive layer consists of a polyvinyl acetate resin selected from the group consisting of vinyl acetate homopolymer vinyl acetate-acrylic acid copolymers, vinyl acetate-acrylic acid ester copolymers, vinyl acetate-vinyl pyrrolidone copolymers, vinyl acetate-vinyl chloride copolymers and vinyl acetate-ethylene copolymers;

the adhesive layer, calculated as the solids, being applied at a rate in the range of about 0.55.0gr./m., based on the area of the stencil paper. 2. A heat-sensitive stencil paper according to claim I, wherein the mol ratio of vinylidene chloride/vinyl chloride in said film is in the range of 7040/ -5.0. 

2. A heat-sensitive stencil paper according to claim 1, wherein the mol ratio of vinylidene chloride/vinyl chloride in said film is in the range of 70-30/95 -5.0. 